1. Field of the Invention
The present invention relates to a printer and, more particularly, to a thermal transfer printer operative to prevent the generation of margins in the upper and lower portions of a sheet of paper, and in which a clearly printed picture can be obtained.
2. Description of the Related Art
A conventional laser printer, which is a type of the thermal transfer printer, comprises a laser head for converting image data into a laser beam and an ink film located below the laser head and holding an ink supply. Using the laser head and ink film, the laser printer carries out printing onto a sheet of paper disposed below the ink film.
In a color laser printer, three resolved images of yellow, magenta and cyan are sequentially printed on a sheet of paper to accomplish full coloring of a completed picture. That is, the paper sheet is printed by the sublimation of ink from the ink film which is heated by the laser beam from the laser head. The printed matter resulting from the color laser printer is extremely sharp. Therefore, the laser printer can be used for various applications. For example, after inputting image data into a computer by an image input device such as a scanner, a newly contrived picture can be created by revising and/or combining the input data according to a computer program and then may be outputted. Also, imaginary scenes and objects created with computer graphics, or the images of an electron microscope may be outputted using the laser printer. As this type of laser printer now tends to be used in lieu of photography in many fields, the printer should have the same quality and form as a photograph.
FIG. 1 illustrates a printing state on a sheet of paper by a conventional printer. As can be seen, a picture 1 is printed on the paper sheet producing margins 2 in the upper and lower portions of the paper sheet.
The causes of the problem of margins will be described hereinafter taking a conventional platen-type printer as an example.
FIG. 2 shows a side view for illustrating a printing operation by a conventional platen-type printer. As can be seen, a sheet of paper 9 supplied from a cassette 13 by a cam 14 passes between a pair of supplying rollers 12 and is transported according to the rotation of a drum 15 while contacting the drum by guide rollers 6 and 7 installed around the periphery of the drum. Paper sheet 9 is transported until the leading edge thereof reaches a guide roller 8 beyond the lower portion of a laser head 10 so that the paper sheet does not become separated from drum 15 during printing. Then, image data is printed on paper sheet 9 by laser head 10 and an ink film 4. Accordingly, a margin equal to a distance D measured from an initial printing position 16 to guide roller 8 is created in the leading edge portion of paper sheet 9. Further, it is difficult to maintain a consistent gap between a luminous element 11 positioned at a lower portion of laser head 10 and the ink film 4, and to precisely transport the paper sheet by the rotation of drum 15 only, which may result in a printed picture of poor clarity and sharpness.
The above-described margins in printed paper sheets and unclear printing causes a low quality appearance in the printed output, thereby resulting in the wasted paper due to the scrapping of poor prints.